Various devices for internal fixation of bone segments in the human or animal body are known in the art. One type of system is a pedicle screw system, which is sometimes used as an adjunct to spinal fusion surgery, and which provides a means of gripping a spinal segment. A conventional pedicle screw system comprises a pedicle screw anchor and a rod-receiving device or coupling member. The pedicle screw anchor includes an externally threaded stem or shank and a head portion. The rod-receiving device couples to the head portion of the pedicle screw and receives an elongate member such as a spinal rod. Two such systems are inserted into respective vertebrae and adjusted to distract and/or stabilize a spinal column, for instance during an operation to correct a herniated disk. The pedicle screw does not, by itself, fix the spinal segment in place, but instead operates as an anchor point to receive the rod-receiving device, which in turn receives the rod. Securing the rod to two or more vertebrae limits the position of the vertebrae with respect to one another, allowing the associated region of the spine to heal or correcting improper positioning of the vertebrae. One goal of such a system is to substantially reduce and/or prevent relative motion between spinal segments that are being fused.
Most pedicle screw systems are “top loading,” wherein a spinal rod is positioned above and perpendicular to the pedicle screw anchor, and then lowered into a channel of the rod receiving device that faces upward from the pedicle screw anchor. Many pedicle screw systems include a threaded locking member that is rotatably inserted into the rod-receiving device on top of the rod after the spinal rod is seated therein in order to fix the position of the spinal rod. Threadless locking members with flanges that are rotated into place to interlock with the rod-receiving device have also been disclosed, such as in U.S. Pat. No. 7,141,051 and U.S. Patent Application No. 2007/0055235. Spinal fixation systems including locking components that require non-rotational linear shifting (such as along the axis of the rod-receiving device) for locking thereof also are known alternatives to utilizing rotatable locking members. Such linearly locking spinal systems are disclosed, for example, in United States Patent Application 2007/0225711, as well as U.S. Provisional Application Nos. 60/784,674 and 60/981,821. These systems include an anchor member (e.g., a screw or hook), a compressible inner tulip member that receives a spinal rod and a pedicle screw head snap-fit thereto, a rigid outer tulip that shifts axially over the inner tulip to compress the inner tulip tightly onto the screw head, and a cap member axially inserted between portions of the inner and outer tulip member to compress the inner tulip about the rod.
Regardless of the manner in which the locking member operates, top loading pedicle screw systems (and other top loading fixation systems such as hook devices) are best manipulated with an instrument capable of grasping the rod receiving device and “reducing” the spinal rod within the rod receiving device (forcing the spinal rod downward to a seated position within the rod-receiving device). Forces imparted on the fixation system and spinal rods by the anatomy of the patient's back, including the positioning and rotation of vertebrae that are to be connected by the fixation system, ordinarily must be overcome to correctly align multiple rod-receiving devices and a spinal rod. As a consequence, significant force must often be applied in order to shift the spinal rod into a fully seated position within the rod-receiving device, allowing the surgeon to correctly secure a locking member to the device and lock the spinal rod therein. Thus, an instrument that can provide a surgeon with a mechanical advantage in shifting the spinal rod into the rod-receiving device is of great benefit. If desired, the same device may also be used to insert and lock the locking member during or after reduction of the spinal rod.
Prior art reducer instruments are often bulky, such as the device disclosed in U.S. Patent Application No. 2003/0225408 which has a side-mounted, lever-actuated clamping mechanism that is secured in position by a laterally-extending rack device. Other devices, such as the device disclosed in U.S. Patent Application No. 2009/0157125, rely on a threaded drive system which requires continual rotation of a drive portion to shift the spinal rod and may have problems with binding of parts. The friction inherent in such threaded drive systems often makes them less than ideal to operate. In addition, cleanability of prior art instruments is often also a concern, since they can have a number of moving parts that may become clogged with blood, tissue, or other materials. Therefore, improved tools for reducing spinal rods and inserting locking members into rod-receiving members are desired.